In the electrical Hall effect, a magnetic field, applied perpendicular to an electrical current, induces through the Lorentz force a voltage perpendicular to the field and the current. It is generally assumed that an analogous effect cannot exist in the phonon thermal conductivity, as there is no charge transport associated with phonon propagation. In this Letter, we argue that such a magnetotransverse thermal effect should exist and experimentally demonstrate this "phonon Hall effect" in Tb3Ga5O12.

We report the first observation of a new optical phenomenon, magnetoelectric directional anisotropy (MEA). MEA is a polarization-independent anisotropy which occurs in crossed electric field E and magnetic field B perpendicular to the wave vector k of the light. It is described by a contribution to the refractive index of the form (delta)n=(gamma)k x E x B. Our experiment was performed on a Er(1.5)Y(1.5)Al(5)O(12) crystal, but MEA should exist in all media. The relation of this new effect with recently discovered magnetoelectric birefringence is discussed.

No abstract

The European Synchrotron Radiation Facility has recently made available to the user community a facility totally dedicated to Time-resolved and Extremeconditions X-ray Absorption Spectroscopy -TEXAS. Based on an upgrade of the former energy-dispersive XAS beamline ID24, it provides a unique experimental tool combining unprecedented brilliance (up to 10 14 photons s À1 on a 4 mm  4 mm FWHM spot) and detection speed for a full EXAFS spectrum (100 ps per spectrum). The science mission includes studies of processes down to the nanosecond timescale, and investigations of matter at extreme pressure (500 GPa), temperature (10000 K) and magnetic field (30 T). The core activities of the beamline are centered on new experiments dedicated to the investigation of extreme states of matter that can be maintained only for very short periods of time. Here the infrastructure, optical scheme, detection systems and sample environments used to enable the mission-critical performance are described, and examples of first results on the investigation of the electronic and local structure in melts at pressure and temperature conditions relevant to the Earth's interior and in laser-shocked matter are given.

Spectroscopy of nuclear resonances offers a wide range of applications due to the remarkable energy resolution afforded by their narrow linewidths. However, progress toward higher resolution is inhibited at modern x-ray sources because they deliver only a tiny fraction of the photons on resonance, with the remainder contributing to an off-resonant background. We devised an experimental setup that uses the fast mechanical motion of a resonant target to manipulate the spectrum of a given x-ray pulse and to redistribute off-resonant spectral intensity onto the resonance. As a consequence, the resonant pulse brilliance is increased while the off-resonant background is reduced. Because our method is compatible with existing and upcoming pulsed x-ray sources, we anticipate that this approach will find applications that require ultranarrow x-ray resonances.

In 1954 Dicke predicted the accelerated initial decay of multiple atomic excitations 1 , laying the foundation for the concept of superradiance. Further studies 2-4 suggested that emission of the total energy was similarly accelerated, provided that the system reaches the inversion threshold. Superradiant emission of the total energy has been confirmed by numerous studies [4][5][6][7][8][9][10][11][12] , yet the acceleration of the initial decay has not been experimentally demonstrated. Here we use resonant diffraction of X-rays from the Mössbauer transition 13 of 57 Fe nuclei to investigate superradiant decay, photon by photon, along the entire chain of the de-excitation cascade of up to 68 simultaneous coherent nuclear excitations created by a pulse of an X-ray free-electron laser. We find agreement with Dicke's theory 1 for the accelerated initial decay as the number of excitations is increased. We also find that our results are in agreement with a simple statistical model, providing a necessary baseline for discussing further properties of superradiance, within and beyond the low-excitation regime. Dicke's model introduces superradiance as an accelerated initial decay of multiple atomic excitations, and provides exact predictions for the ensemble behaviour as a function of the number of atoms and number of excitations in the system

Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Lummen, T. T. A., Strohm, C., Rakoto, H., Nugroho, A. A., & van Loosdrecht, P. H. M. (2009 Pulsed-field magnetization experiments extend the typical metamagnetic staircase of CuFeO 2 up to 58 T to reveal an additional first-order phase transition at high field for both the parallel and perpendicular field configuration. Virtually complete isotropic behavior is retrieved only above this transition, indicating the high-field recovery of the undistorted triangular lattice. A consistent phenomenological rationalization for the field dependence and metamagnetism crossover of the system is provided, demonstrating the importance of both spin-phonon coupling and a small field-dependent easy-axis anisotropy in accurately describing the magnetization process of CuFeO 2 . Metamagnetism typically refers to any material that, upon variation in the externally applied magnetic field, exhibits an abrupt change in magnetization. In general, the phase diagrams of materials undergoing field-induced magnetic transitions can be rationalized according to the degree of magnetic anisotropy in the materials.1 In highly anisotropic systems, spins are effectively restricted to align ͑anti͒parallel to the magnetic easy-axis and magnetic transitions typically involve discontinuous spin reversals, leading to first-ordertype metamagnetic transitions. As for isotropic ͑weakly anisotropic͒ systems this directional restriction is relieved ͑strongly reduced͒, transitions in such materials often reflect the onset of a continuous, second-order-type reorientation of the local spins. Another source of exotic magnetic transitions is geometrical magnetic frustration, which occurs when a specific lattice geometry prevents the simultaneous minimization of all magnetic exchange interactions, thus introducing a high spin degeneracy.2 The simultaneous occurrence of both these phenomena and the interplay between them leads to intricate, diverse, and rich physics, yielding many captivating magnetic phases ranging from spin liquids and ices to multiferroic spiral phases. [3][4][5][6] Here the focus is on the delafossite semiconductor CuFeO 2 , an arche-type triangular lattice antiferromagnet, in which the Fe 3+ ions stack in hexagonal layers along the c axis ͓Fig. 1͑a͔͒. In spite of the expected Heisenberg nature of the Fe 3+ spins ͑3d 5 , S =5/ 2, and L =0͒, CuFeO 2 does not order in the noncollinear 120°spin configuration at low temperature. Instead, after undergoing successive phase transitions at T N1 Ϸ 14 K and T N2 Ϸ 11 K, lowering the symmetry from hexagonal ͑R3m͒ to monoclinic, 7-9 the system adopts a collinear, two-up two-down order, with moments aligned ͑anti͒parallel along the c axis ͓Fig. 1͑b͔͒ ͑Ref. 10͒. The collinear ground state is supposedly stabilized through the strong spin-lattice coupling in CuFeO 2 , 7-9,11 which induces a structural distortion through the "spin Jahn-Teller" effect. 12,13 Alternatively, this scalene triangle distorti...

The magnetic phase diagram of CuFeO2 as a function of applied magnetic field and temperature is thoroughly explored and expanded, both for magnetic fields applied parallel and perpendicular to the material's c-axis. Pulsed field magnetization measurements extend the typical magnetic staircase of CuFeO2 at various temperatures, demonstrating the persistence of the recently discovered high field metamagnetic transition up to TN2 ≈ 11 K in both field configurations. An extension of the previously introduced phenomenological spin model used to describe the high field magnetization process (Phys. Rev. B, 80, 012406 ( 2009)) is applied to each of the consecutive low-field commensurate spin structures, yielding a semi-quantitative simulation and intuitive description of the entire experimental magnetization process in both relevant field directions with a single set of parameters.